Vesicular and non-vesicular transport feed distinct glycosylation pathways in the Golgi

Glucosylceramide (GlcCer), a common precursor of different glycosphingolipids, is shown to be channelled to two distinct pathways in the Golgi; non-vesicular transport from the cis - to trans -Golgi network results in the synthesis of the globo series of glycosphingolipids, whereas vesicular transport is the main source of GlcCer for ganglioside synthesis in the Golgi cisternae. Dual carriageway in the Golgi transport complex Newly synthesized lipids are transported across the Golgi network through vesicular and non-vesicular mechanisms. This study demonstrates that glucosylceramide (GlcCer), which is the common precursor of various glycosphingolipids, is channelled to two topologically distinct pathways in the Golgi. Non-vesicular transport of GlcCer from its site of synthesis in the cis -Golgi to the trans -Golgi results in the synthesis of the globo-series (Gb3) of glycosphingolipids, whereas vesicular transport is the major source of GlcCer for the synthesis of gangliosides in the Golgi cisternae. Newly synthesized proteins and lipids are transported across the Golgi complex via different mechanisms whose respective roles are not completely clear. We previously identified a non-vesicular intra-Golgi transport pathway for glucosylceramide (GlcCer)—the common precursor of the different series of glycosphingolipids—that is operated by the cytosolic GlcCer-transfer protein FAPP2 (also known as PLEKHA8) (ref. 1 ). However, the molecular determinants of the FAPP2-mediated transfer of GlcCer from the cis -Golgi to the trans -Golgi network, as well as the physiological relevance of maintaining two parallel transport pathways of GlcCer—vesicular and non-vesicular—through the Golgi, remain poorly defined. Here, using mouse and cell models, we clarify the molecular mechanisms underlying the intra-Golgi vectorial transfer of GlcCer by FAPP2 and show that GlcCer is channelled by vesicular and non-vesicular transport to two topologically distinct glycosylation tracks in the Golgi cisternae and the trans -Golgi network, respectively. Our results indicate that the transport modality across the Golgi complex is a key determinant for the glycosylation pattern of a cargo and establish a new paradigm for the branching of the glycosphingolipid synthetic pathway.